UPDATE:  I am updating this post with information from my trip to Botswana in January, 2015.  

Here are some statistics from the trip.  As of the date of this writing I have posted 159 images to the galleries.

Here is a summary of images by camera and lens:

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As you can see, from my selects, 31% were taken with the 7d mark II.  And of the total images (159) taken with all bodies, 36% were taken with the 100-400.  I also found it interesting that of my 7d markII images, 28% were with the 100-400 and 72% used the 200-400.

Here are two examples:

100-400:

Cubs at the Water HoleVumbura Plains Camp, Okavango Delta, Botswana

200-400:

Lion Paws are Huge

My conclusions:  Both the 100-400 and 200-400 will stay in my kit.  I will choose the lens primarily based on anticipated light and amount of weight I want to carry.  Image sharpness is outstanding on both lenses.

I will also keep the 7d mark II in my kit.  While I feel the 1dx images are more pleasing, there is nothing wrong with the 7dII, particularly when more "reach" is needed.  I feel very comfortable with this body and either lens up to 1600 iso.

End of UPDATE

Begin original post:

First of all, this is NOT a lens or camera review.  Canon has "completed" their lens lineup, at least so far as I am concerned for the photography I do. In the past few years, they have released the 200-400 and, recently, an updated 100-400.  So, I have looked at both of these lenses in the context of how I shoot and thinking about the subjects I shoot.  So, for me, the comparison is the 200-400 on a 1DX and the 100-400 on the new 7D mark 2.

Understanding that we are comparing gear that lists for $18,598 vs. $3,998 I still think it is worthwhile for the following reasons:  First, the 200-400/1dX weighs 12 pounds on my trusty postal scale compared to 7 pounds for the 100-400/7d2.  Five pounds might not seem like a lot, but it is, particularly for hand held.  Second, the focal length ranges are roughly comparable.  The 200-400/1dx gets out to 560mm with the built in teleconverter and has a maximum aperture of f/5.6.  The 100-400/7d2 get out to 640mm at a maximum aperture of f/5.6.  So, from a light gathering and reach perspective they are reasonably close.  Third, I owned the old 100-400 and didn't like the sharpness after about 350mm so I sold it.  Lately my go to hand held is the 70-300, which the new 100-400 seems to be of similar design.

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So, in order to decide when I will use one vs the other I took my trusty moving subject, Darby the Wonder Dog, out for training this morning and made some images of her retrieving.  

One other factor that is important to me is the higher ISO performance.  I have no qualms about setting the ISO to 1600 on the 1dx and usually don't have to apply any noise reduction.  I will even go higher if I need to for the image but then noise reduction comes in.  On my old 7d I wouldn't go above 800, which is one of the reasons I sold it.  It seems that the places I go and images I make often require the higher ISO to get the DOF and shutter speed I want.

So, having said all this, what are my impressions.  First, both cameras are wonderful operationally.  Twelve FPS on the 1dx and 10 FPS on the 7d2 with auto focus that is more than adequate for my needs on both cameras.  Image quality is better, I believe, on the 1dx, particularly at 1600 ISO and above.  It seems like noise reduction will be required on the 7d2 at 1600 and above.  Having said that, the weight difference makes it easier to hand hold the 100-400/7d2.  So, my conclusion is that the 100-400/7d2 will find its way into my bag on most of the trips I go on.  Another advantage is that the 7d2 will also go on the 200-400, giving me almost 900mm.

I thought it was interesting that in his blog Scott Kelby called the 100-400 a "daytime" lens due to the maximum aperture.  I would call the combo a daytime combo if you want to shoot at 800 ISO or less.

We are going to Botswana in January.  I will be leaving the 600 at home and bring both the 200-400 and 100-400, along with the two bodies.

Here are a couple of images illustrating my points above:

Darby with the 100-400/7d2

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Darby with the 200-400/1dx and internal 1.4 t/c:

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Lightroom screen grab comparing both images at 100%:

7d2 on the left.

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I'm not sure you can see how great the difference is in this post, but the noise, particularly on the dummies and background is quite noticeable.  I applied a small amount of noise reduction in Lightroom but there is still a difference.

Back the original title of this post.  The 100-400 appears to be a significant upgrade.  It works similar to my 70-300 with the twist zoom.  It seems to be very sharp and focuses quickly with the bodies I own.  I expect the 200-400/1dx on a bean bag will be my most used combo in Africa, but I'll have a more informed opinion when I get back at the end of January. The 100-400 will likely replace the 70-300 for travel and my intermediate carry zoom on my photo adventures.  It is heavier, but the extra 100mm of reach offsets that in my mind.  I'm still not set yet on the 200-400 as my longest lens, but will be giving it a good workout with the 7d2.  For what I shoot, 900 mm is usually more than I need.